HK1221775B - Dynamic appearance-changing optical devices (dacod) printed in a shaped magnetic field - Google Patents

Description

Optical patterns printed in a shaped magnetic field that dynamically change appearance

This application is a divisional application of the Chinese invention patent application with application date of April 6, 2006, application number 201210196872.0, and invention name “Optical pattern with dynamically changing appearance printed in a forming magnetic field”.

Technical Field

The present invention relates generally to optically variable pigments, films, patterns and images, and more particularly to aligning and orienting magnetic flakes to produce an illusive optical effect, such as during a coloring or printing process.

Background Art

Optically variable patterns are widely used in a variety of decorative and practical applications, for example, as anti-counterfeiting features on commercial products. Optically variable patterns can be manufactured using a variety of methods to achieve a variety of effects. Examples include holograms embossed on credit cards and genuine software files, color-shifting images printed on banknotes, and enhancing the surface appearance of items such as motorcycle helmets and wheel covers.

Optically variable patterns can be manufactured as films or foils that are printed, embossed, bonded, or otherwise adhered to an object. They can also be produced using optically variable pigments. One type of optically variable pigment is commonly known as a color-shifting pigment, because the apparent color of an image properly printed with such a pigment changes with viewing angle and/or tilted lighting angle. A common example is the "20" printed with color-shifting pigment in the lower right corner of the US twenty-dollar bill, which serves as a security feature.

Some security features are covert, while others are designed to be noticeable. However, some optically variable features designed to be noticeable are not widely recognized because the optically variable aspect of the feature is not sufficiently noticeable. For example, the color change of an image printed with color-shifting pigments under uniform fluorescent overhead lighting is unnoticeable, but may be more noticeable under direct sunlight or single-point lighting. This makes it easier for counterfeiters to pass inspection on counterfeit notes without optically variable features because the recipient may not be aware of the optically variable feature or because counterfeit notes can appear substantially similar to genuine notes under certain conditions.

Optically variable patterns can also be made using magnetic pigments, which are aligned using a magnetic field after the pigment (usually in, for example, an ink carrier or paint vehicle) is applied to the surface. However, coloring with magnetic pigments is mostly for decorative purposes. For example, the use of magnetic pigments to make painted wheel covers with decorative features that appear as three-dimensional shapes has been described. The pattern is formed on the painted product by applying a magnetic field to the product while the paint medium is still in a liquid state. The paint medium has dispersed magnetic non-spherical particles aligned along the lines of the magnetic field. The field has two regions. The first region contains magnetic lines of force that are oriented parallel to the surface and are arranged in the shape of the desired pattern. The second region contains lines that are not parallel to the surface of the painted product and are arranged in a surrounding pattern. To form the pattern, a permanent magnet or electromagnet having a shape corresponding to the desired pattern is located below the painted product so that the non-spherical magnetic particles dispersed in the paint are oriented in the magnetic field while the paint is still wet. When the paint dries, the pattern becomes visible on the surface of the painted product as light incident on the paint layer is affected differently by the oriented magnetic particles.

Similarly, a process for creating patterns of flake-like magnetic particles in a fluoropolymer matrix has been described. After coating the product with a liquid component, a magnet with a magnetic field of the desired shape is placed beneath the substrate. The magnetic flakes dispersed in the liquid organic medium orient themselves parallel to the magnetic field lines, tilted relative to their initial planar orientation. This tilt changes from perpendicular to the substrate's surface to an initial orientation that includes flakes that are essentially parallel to the product's surface. The planarly oriented flakes reflect incident light back to the viewer, while the reoriented flakes do not, giving the appearance of a three-dimensional pattern in the coating.

It is an object of the present invention to provide optically variable images in which magnetically alignable pieces, such as three-dimensional objects such as hemispheres, cones, etc., are used to form images of pseudo patterns, labels, etc. under specific magnetic fields not described heretofore.

Summary of the Invention

The present invention provides an article, method and apparatus relating to images having illusory optical effects.

According to the present invention, there is provided a security pattern comprising a first plurality of magnetically alignable flakes resting on a substrate in a first pattern so as to define an image of a loop or curve. Preferably, there are at least n flakes, assuming n > 1000, and wherein planes extending from surfaces of the flakes intersect one another.

According to one embodiment of the present invention, the first plurality of magnetically alignable sheets define a plurality of concentric rings of sheets, and the rings of sheets form a circular area; the sheets defining the rings form increasing or decreasing angles relative to the base from the outermost ring to the innermost ring.

In one aspect of the invention, the pattern may comprise a second plurality of magnetically alignable flakes stationary on a substrate in a pattern corresponding to the first pattern, wherein the flakes are tilted at the same second angle relative to the substrate, wherein the second angle is different from the first angle, and wherein faces extending from surfaces along the second plurality of flakes intersect one another.

The plurality of magnetically alignable flakes may be distributed substantially throughout the enclosed area and oriented therein in a predetermined pattern, wherein at least greater than 50% of the flakes are oriented such that lines perpendicular to their reflective surfaces converge along a line or to a point.

In a preferred embodiment, the image comprises at least 10,000 slices or more.

According to one aspect of the present invention, there is provided an optical illusion image comprising a substrate having an area of flakes coated on a surface thereof, wherein the flakes are distributed substantially throughout the area and oriented in a predetermined pattern therein, wherein the flakes are oriented such that lines perpendicular to their reflective surfaces converge along the line or to a point.

According to another aspect of the present invention, there is provided a label or security pattern comprising an optically illusory image having flakes covering and distributed over an entire area and oriented in a predetermined pattern, the flakes having a reflective surface, wherein the orientation of the flakes forming the predetermined pattern is such that lines perpendicular to their reflective surfaces converge along a line or to a point, wherein the predetermined pattern has an axis of rotation.

According to another aspect of the present invention, a printed array is provided comprising a plurality of concentric rings of magnetically aligned platelets disposed on a substrate in the form of a Fresnel structure, preferably a Fresnel reflector. Advantageously, because the strength and direction of the magnetic field can be controlled, it is easy to design a field that corrects for spherical aberration, which is present to varying degrees in typical Fresnel reflectors.

According to one aspect of the invention, the image forms part of a receiving or reflecting antenna and wherein the foil is a selectively absorbing or reflecting foil, respectively.

According to another aspect of the invention, the optical image described in any of the embodiments described hereinbefore has a grating thereon and/or has flakes having a surface area of 100 μm ² to 1 mm ² and wherein the thickness of the flakes is in the range of 100 nm to 100 μm.

According to another aspect of the present invention, at least some of the flakes have gratings therein or thereon, wherein the frequency and depth of the gratings are sufficiently low so as not to have a diffraction effect visible to the human eye, and wherein the flakes having the gratings are aligned along the lines of the respective gratings. In some embodiments, at least some of the flakes have gratings therein or thereon, wherein the frequency of the gratings is less than 200 lines/mm, and wherein the depth of the gratings is less than 100 microns.

The flakes are uniform in shape, preferably hexagonal to allow for greater packing density.

In an alternative embodiment of the invention, an image is provided which forms a light detector, the image being dynamic such that it displays a plurality of rings corresponding to a plurality of independent light sources illuminating the image.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described according to the present invention, wherein:

FIG. 1A is a simplified cross-sectional view of a printed image known as a "flip-flop" as described and shown in applicant's US patent application US 2005/0106367 A1.

FIG. 1B is a simplified plan view of a printed image on a document as described and shown in applicant's US patent application US 2005/0106367 A1 as viewed from a first selected viewing angle.

FIG. 1C is a simplified plan view of a printed image described and shown in applicant's US patent application US 2005/0106367 A1 viewed at a second selected viewing angle, the simplified plan view being obtained by tilting the image relative to the viewpoint.

FIG. 2A is a simplified cross-sectional view of a printed image, referred to for discussion purposes as a “scroll bar,” which is described and illustrated in applicant's US patent application US 2005/0106367 A1.

FIG. 2B is a simplified plan view of a scroll bar image viewed from a first selected viewing angle as described and shown in applicant's US patent application US2005/0106367A1.

FIG. 2C is a simplified cross-sectional view of a printed image referred to for discussion purposes as a “double scroll bar,” which is described and illustrated in applicant's US patent application US 2005/0106367 A1.

FIG. 2D is a top view of the image shown in FIG. 2C .

3 is a cross-sectional view of magnetically aligned platelets in a printed dry ink layer corresponding to the star burst image shown in FIG. 4 .

FIG. 4 is a plan view of an image of a starburst pattern according to the present invention.

5A and 5B are photographs of images of cones composed of magnetically aligned platelets.

FIG6 is a cross-sectional view of a conical magnetic field showing the platelets aligned in the field.

FIG. 7A is a photograph of a cone image when viewed from directly above at an angle perpendicular to the image surface.

7B and 7C are photographs of cone images observed from different angles.

8 is a cross-sectional view of an alternative embodiment of the present invention in which two annular stacked magnets having different radii are used to generate a novel magnetic field that has surprising effects in the printed image.

FIG. 9 is a photograph of an image produced by magnetic alignment using the method of FIG. 8 .

10A, 10B, 10C, 11, 12, and 13A are images of inks containing magnetic particles used in various patterns, with a circular magnetic field used to align the magnetic platelets.

FIG. 13B is a photograph of an optically illusion image according to the present invention.

14 is a diagram showing the arrangement of slices in the cone image shown in FIG. 7B ; for illustration purposes, larger and fewer symmetrical slices are employed, and some slices are purposefully omitted to show a side view of a particular slice.

FIG. 15 is a diagram similar to FIG. 14 shown in perspective.

FIG. 16 is a diagram similar to FIG. 15 showing the axial alignment of non-structured magnetic platelets dispersed in the ink layer along the magnetic field lines of an applied conical magnetic field.

17 is a diagram of a conical arrangement of magnetic particles dispersed in a vehicle or carrier of a thin layer of ink showing that the angles normal to the particle surface converge above the image along a curve defining an imaginary loop.

18A and 18B are photographs showing diagrams of reflective rings having a conical arrangement.

FIG. 19 is a diagram showing the conical arrangement of magnetic particles in a conical magnetic field when a conical magnet is positioned on a substrate.

20A is a diagram of the conical arrangement of magnetic particles in a conical magnetic field when a funnel-shaped magnet is located beneath a substrate.

FIG. 20B is a photograph of an image of a funnel-shaped object according to the present invention.

20C is a partial cross-sectional view of a funnel-shaped arrangement of magnetic platelets dispersed in a vehicle comprising a thin layer of ink having surfaces perpendicular to the illustrated particles.

20D is a cross-sectional view of the funnel-shaped arrangement of magnetic particles in a funnel-shaped magnetic field when a spherical magnet is located beneath the substrate.

21A and 21B are photographs of images obtained from the particle arrangement shown in FIG. 20A .

FIG22 is a partially cutaway perspective view of an arrangement of diffracting magnetic particles in an axisymmetric conical magnetic field.

Figures 23 and 24 are photographs of axisymmetric prints containing magnetic diffractive particles and tilted towards the viewer.

25 is a diagram showing the orientation of a diffractive flake when placed in a magnetic field, where the grooves of the flake are shown parallel to the magnetic field lines.

26 is a diagram of an axisymmetric hemispherical arrangement of magnetic particles dispersed in a thin layer of ink, forming a printed convex Fresnel mirror.

27 is a cross-sectional view of the Fresnel mirror shown in FIG. 26 showing that lines perpendicular to the sheet converge toward a point along the line.

28A and 28B are photographs of a hemispherical convex mirror.

29 is a diagram of an axisymmetric arrangement of magnetic particles dispersed in an ink layer along the magnetic field lines of an applied hemispherical magnetic field, forming a printed non-compensated convex Fresnel reflector.

FIG30 is a diagram showing the arrangement of diffraction particles dispersed in an ink layer.

Figure 31 is a photograph of a printed convex Fresnel mirror made with diluted ink on a black background.

FIG. 32 is a diagram showing an axisymmetric hemispherical arrangement of magnetic particles dispersed in a thin layer of ink printed on a substrate.

33 is a diagram showing a concave arrangement of magnetic diffraction particles 333 having a groove-shaped grating therein, the magnetic diffraction particles being dispersed in a thin layer of an ink vehicle 332 with lines perpendicular to the particle surfaces 334. FIG.

34A, 34B, and 34C are photographs of hemispherical array images.

FIG35 is a plan view of an axisymmetric concave arrangement of diffractive magnetic particles dispersed in an ink layer, which is similar to FIG29 in many respects.

FIG36 is a diagram showing the position and arrangement of diffraction particles in a single radial line of particles dispersed in an ink layer.

FIG. 37A is a perspective view of a magnet constituting the magnet structure shown in FIG. 37C for providing the dome-shaped magnetic field shown in FIG. 37C .

Figure 37B is a perspective view of the magnet shown in Figure 37A when rotated about its vertical axis. For illustrative purposes, the magnet is shown at two different moments in its rotation in order to understand how the hemispherical magnetic field is formed.

37C is a perspective view of the same magnet at three angles of rotation after the magnet completes one rotation about the vertical axis.

37D is a perspective view of the magnet arrangement of FIG. 37C wherein a plate with an ink flake is positioned in a dome-shaped field and wherein the plate and field are rotated relative to each other as shown by the arrows in two consecutive figures.

37E is a perspective view similar to FIG. 37D , wherein the plate is positioned near the top of the dome-shaped field, and wherein the size of the hemispherical image formed in the ink is smaller than in FIG. 37D .

37F and 37G are images of a rolling 3D hemisphere made using the magnets of FIG. 37E , showing the image at different positions as it is tilted from one position to another.

FIG37H is a printed image of a hemisphere with dome-shaped flakes disposed in the image of a shield.

FIG371 is a printed image of a shield having scroll bars formed along its axis.

Figure 37J is a composite image of the images formed in Figures 37H and 37I, where the ink and magnetic field are applied in multiple steps, thereby applying Figure 37I over Figure 37H, and where the center area is coated only once when forming the rolling hemisphere.

FIG38A is a cross-sectional view of the bowl-shaped field used to form the image of FIG38C.

38B is a cross-sectional view of pigment flakes in a carrier aligned in the magnetic field shown in FIG. 38A.

FIG38C is an image formed with magnetic flakes in the field shown in FIG38A of an inverted hemisphere that appears as a rolling bowl recessed in the page.

FIG39 is a plan view of a single particle of a microstructured magnetic pigment.

FIG40 is a cross-sectional view of a single particle of a microstructured magnetic pigment.

FIG41 is a structural diagram of _MgF2 /Al/Ni/Al/MgF2 _multilayer magnetic microstructure pigment.

Figures 42a and 42b are multi-angle color trajectory diagrams showing a low-modulated low-frequency rectangular grating (1) and a high-frequency sinusoidal grating (2) in the measurement direction along the groove.

Figure 43 shows the spectral reflectivity of an optical film stack _MgF2 /Al/Ni/Al/ _MgF2 deposited on top of a low modulation (80 nm) low frequency (140 lines/mm) rectangular grating.

FIG44 shows the spectral reflectance of the optical film stack _MgF2 /Al/Ni/Al/ _MgF2 deposited on top of low frequency (140 lines/mm).

DETAILED DESCRIPTION

Various embodiments of the present invention provide novel and inventive magnetic field structures for use in anti-counterfeiting, packaging, and labeling applications. Typically, when printing or coloring a surface, particles of optically variable pigments dispersed in a liquid coating or ink vehicle are typically oriented parallel to the surface. This orientation parallel to the surface results in a high reflectivity for incident light from the coated surface. When a magnetic field is applied in a liquid medium, the magnetic flakes can be tilted relative to the substrate. The flakes are typically arranged so that the longest diagonal of the reflective flakes and the grooves of the diffractive flakes are oriented to follow the magnetic field lines. Depending on the position and strength of the magnets, the magnetic field lines can pass through the substrate at different angles, tilting the magnetic flakes to these angles. Tilt flakes reflect incident light differently from flakes parallel to the printed substrate surface. Both the reflectivity and the color can be different. When viewed from a normal viewing angle, tilted flakes typically appear darker and have a different color than flakes parallel to the surface.

Example of printing an illusory image

Figure 1A is a simplified cross-sectional view of a printed image 20A according to one embodiment of the present invention, referred to for discussion purposes as a "switching" optical effect image or "flipped" image. The flipped image includes a first printed portion 22 and a second printed portion 24, separated by a transition portion 25. Pigment flakes 26, enclosed by a carrier 28, such as an ink vehicle or paint vehicle, are aligned parallel to a first plane in the first portion, while pigment flakes 26' in the second portion are aligned parallel to a second plane. The flakes are represented as short lines in the cross-sectional view. The flakes are magnetic, meaning they can be aligned using a magnetic field. They may or may not retain residual magnetism. Not all flakes in each portion are exactly parallel to one another or to their respective alignment planes, but the overall effect is essentially as shown. The figures are not drawn to scale. Typical flakes may be 20 microns wide and approximately 1 micron thick, so the figures are provided for illustrative purposes only. The image is printed or colored on a substrate 29, such as paper, plastic film, sheet, card, or other surface. For ease of discussion, the term "printing" is generally used to describe the application of pigments in a carrier to a surface, although it may include other techniques, which may be referred to as "painting."

Typically, the flakes appear light when viewed perpendicular to the plane of the flake and dark along the edges. For example, light from illumination source 30 is reflected from the flake in a first region toward viewer 32. If the image is tilted, as indicated by arrow 34, the flake is viewed end-on in first region 22, while light is reflected from second region 24. Thus, at a first viewing position, the first region is light and the second region is dark, while at a second viewing position, the field is reversed, with the first region dark and the second region light. This provides a distinct visual effect. Similarly, if the pigment flakes are color-shifting, one portion can appear one color and another portion can appear another color.

The carrier is typically transparent, either clear or tinted, and the flakes are typically quite reflective. For example, the carrier can be dyed green, and the flakes can include a metal layer, such as a thin film of aluminum, gold, nickel, platinum, or a metal alloy, or a metal flake, such as nickel or an alloy. Light reflected from the metal layer through the green-dyed carrier can appear bright green, while another portion with the flakes, viewed end-on, will appear dark green or another color. If the flakes are simply metal flakes in a clear carrier, one portion of the image can appear bright metallic, while another portion is dark. Alternatively, the metal flakes can be coated with a dyed layer, or the flakes can include an optical interference structure, such as an absorber-spacer-reflector Fabry-Perot structure. Furthermore, diffractive structures can be formed on the reflective surface to provide enhanced and additional security features. The diffractive structure can be a simple linear grating formed in the reflective surface, or a more complex, predetermined pattern that is discernible only under magnification but has an overall effect when viewed. By providing a diffractive reflective layer, a change in color or brightness can be seen by the observer by simply rotating the paper, banknote or structure with diffractive flakes.

The process for making diffractive flakes is described in detail in U.S. Patent No. 6,692,830. U.S. Patent Application 20030190473 describes the fabrication of colored diffractive flakes. The production of magnetic diffractive flakes is similar to that of diffractive flakes, however, one of the layers must be magnetic. In practice, the magnetic layer can be masked by sandwiching it between aluminum layers; in this manner, the magnetic layer has essentially no effect on the optical design of the flake, or it can simultaneously contribute optically to the thin-film interference optical design by acting as an absorber, dielectric, or reflector.

FIG1B is a simplified plan view of a printed image 20 on a substrate 29, viewed from a first selected viewing angle, which may be a document such as a banknote or stock certificate. The printed image may serve as a security and/or authentication feature because the illusory image cannot be photocopied or produced using conventional printing techniques. The first portion 22 is light and the second portion 24 is dark. Section line 40 represents the cross-section shown in FIG1A. The transition portion 25 between the first and second portions is relatively sharp. The document may be, for example, a banknote, stock certificate, or other valuable printed article.

FIG1C is a simplified plan view of printed image 20 on substrate 29, viewed from a second, selected viewing angle, obtained by tilting the image relative to the viewpoint. First portion 22′ is now dark, while second portion 24′ is light. The tilt angle at which the image flips depends on the angle between the planes of arrangement of the sheets in different portions of the image. In one example, the image changes suddenly from light to dark when tilted approximately 15 degrees.

FIG2A is a simplified cross-sectional view of a printed image 42 of a moving optical pattern according to another embodiment of the present invention, which for discussion purposes is defined as a microscopic array of columnar Fresnel reflectors or "rolling bars." The image includes pigment flakes 26 surrounded by a transparent carrier 28 printed on a substrate 29. The pigment flakes are arranged in a curvilinear pattern. As the image is flipped, the areas of the rolling bars that reflect light from the faces of the pigment flakes toward the viewer are brighter than areas that do not directly reflect light toward the viewer. The image has Fresnel focal lines that look very much like bands or strips of light, and they appear to move ("roll") along the image when the image is tilted relative to the viewing angle (assuming a fixed illumination source).

FIG2B is a simplified plan view of scrolling bar image 42 viewed from a first selected viewing angle. Bright bar 44 appears at a first position in the image, between two contrasting areas 46 and 48. FIG2D is a simplified plan view of the scrolling bar image viewed from a second selected viewing angle. Bright bar 44' appears to have "moved" to a second position in the image, and the sizes of contrasting areas 46' and 48' have also changed. As the image is tilted (at a fixed viewing angle and fixed lighting), the arrangement of the pigment flakes creates the illusion that the light bar "rolls" downward from the image. When the image is tilted in the other direction, the light bar appears to roll in the opposite direction (upward).

A light stripe can also appear to have depth even though it is printed in a flat surface. The actual depth may appear to be significantly greater than the physical thickness of the printed image. This occurs because the light stripe is an illusory focal line of a cylindrical convex Fresnel reflector, which is located at a focal length below the plane of the reflector. The flakes are tilted in a pattern selected to reflect light to provide what is commonly referred to as the illusion of depth or "3D". A three-dimensional effect can be achieved by using magnetic pigment flakes on a base of a liquid carrier, with a shaped magnet placed behind the paper or other substrate. The flakes align along the magnetic field lines and produce a 3D image after the carrier is processed (e.g., dried or cured). As the carrier is tilted, the image often appears to move; thus, a 3D image with movement can be created.

Can print turnover and rolling strip with magnetic pigment flake, promptly can use magnetic field to arrange pigment flake.The turnover type image of printing has the optically variable pattern with two different zones, and it can use single printing step and use single ink formula to obtain.The rolling strip type image has the optically variable pattern, and it has the contrast band that moves along with the image tilt, is similar to the semi-precious stone that is called tiger eye.The image of these printings is very noticeable, and this illusory appearance can not be photocopied.These images can be used for banknote, stock certificate, software file, anti-counterfeiting seal and similar object as identification and/or anti-counterfeiting pattern.For the large amount of printed documents of for example banknote, packaging and label, these images need especially, because these images can be printed in high-speed printing operation as described below.

In another embodiment, a "double rolling bar," as shown in Figures 2C and 2D, is an image in which one portion 44' has magnetic flakes oriented in a cylindrical convex manner, while another portion 44" of the image has magnetic flakes oriented in a cylindrical concave manner. To obtain a convex orientation, the "rolling bar" magnets are placed below the paper substrate. For a concave orientation, the magnets are placed above the paper substrate. When the magnetic flakes in two areas of the image have different and opposite orientations, such as +30 degrees and -30 degrees, a "double tilt" image is formed. At one tilted position of the printed image, one portion of the image is dark and the other portion is light. . When the printed images are tilted in opposite directions, the areas will switch their light and dark areas, making the first image lighter and the second darker. Depending on the desired design, this switching of light and dark can occur from top to bottom and vice versa, or from left to right and vice versa, depending on the orientation of the sheet. In Figures 2C and 2D, the light bar 44' appears to have "moved" to a second location in the image, and the size of the contrasting areas 46', 48' has changed; and the light bar 44" appears to have "moved" to a different location in the image, and the size of the contrasting areas 46", 48" has changed.

The present invention applies a three-dimensional magnetic field having a predetermined shape for continuous or discrete printing of dynamically changing optical patterns (DACODs). Dynamic optical patterns are images, some of which can be printed using high-speed printers, using ink containing magnetic flake-shaped pigments in a magnetic field having a predetermined shape. The images are able to change their appearance in response to physical actions applied to the substrate by an observer. The observer needs to tilt, rotate, or bend the substrate to see part or all of the image appear, disappear, or move. This appearance of the dynamically changing optical pattern depends solely on the reflection or scattering of incident light from the differently oriented magnetic flakes in the dry ink layer. The presence or absence of color is a supplementary feature of DACODs. In addition to their changing appearance, magnetic color-changing pigments have a variety of variations in the color changes of the dynamic optical pattern.

This invention describes a special type of dynamic optical pattern. In a portion of an image printed on paper or other flat substrate material by screen printing, offset printing, rubber printing, gravure printing, intaglio printing, or other known printing methods, and in a magnetic field of varying configurations, the printed image is printed in such a way that, during the transition of the wet image printed on the substrate in the field, the pigment flakes in the ink layer align along the magnetic field lines of the field, causing the image to change its appearance when viewed at different angles after the ink dries. The printed image with a variable appearance component does not require any special equipment for viewing, so it can be viewed with the naked eye. Printing a dynamic optical pattern at different angles relative to a light source causes a noticeable change in appearance or movement of the portion of the image printed with magnetic ink. The ink used for the dynamic optical pattern consists of an ink vehicle and any light-reflecting or light-scattering platelet-based magnetic pigment. The pigment can be a color-shifting pigment, a non-color-shifting pigment, and/or have a microstructure, such as a diffraction grating, that facilitates the orientation of the magnetically aligned flakes. The ink vehicle can be clear or pigmented, UV-curable, or solvent-based.

Printed optical patterns that change appearance can be used as security features on or in banknotes and securities.

Effects that appear to move or change within an image are well known in the printing industry. Moving effects are often based on a specific image or set of patterns, or effects that change with flipping an image are based on a lenticular substrate. Known effects are limited in number, which significantly limits their applicability.

Images that change appearance when printed in a magnetic field have been previously described in the applicant's previously published U.S. Patent No. 2004/0051297A1. Described therein are printed images with rolling bar and flipping effects, which vary the color or intensity of reflected light in different parts of the image as the light source and viewing angle change. For holographic or embossed substrates, the change in image appearance due to these effects is not instantaneous, but rather occurs gradually.

While the image described in the previously mentioned '297 U.S. patent application relates to a simple roll-and-flip type application, wherein the flakes along a single straight line are symmetrical and at the same angle to the substrate; the flakes along the next adjacent straight line are at different angles to the substrate, such that each flake in a given row of flakes is at the same angle to the substrate, and wherein flakes in adjacent rows generally form different angles to the substrate.

We have recently discovered that by arranging flakes along curves, wherein the flakes along any given curve form the same angle with the base, and wherein the flakes along adjacent curves, particularly adjacent circles, and particularly concentric circles, are oriented to form different angles compared to the adjacent curves or circles, it is possible to form distinct, realistic optical illusions of objects such as funnels, cones, bowls, and ellipses and hemispherical shapes. It should be noted that in particular embodiments, the circles may be slightly more elliptical than circular, and that the definition of circle hereinafter includes circular rings and shapes.

The following description refers to distinctly different kinds of printed optical effects, which resemble the reflection of incident light through reflective cones, spheres, hemispheres, funnels, and various other three-dimensional objects, particularly Fresnel-like structures.

Examples are shown below, where FIG4 is an image with a dynamic effect in the form of a starburst pattern; FIG5A shows an image of a cone, and FIG20B shows an image of a funnel. Prints with "starburst" images are produced using a funnel-shaped magnetic field. FIG3 shows a cross-sectional view of the orientation of flakes in a printed dry ink layer. Ink 192 containing dispersed magnetic particles 193 is printed on top of a substrate 191 using one of the printing methods described above. Magnetic field lines 194 at the center of the image are oriented perpendicular to the substrate. The magnetic field lines decrease with increasing radial distance from the center; thus, the field is strongest at the center and weakens radially outward from the center.

The center of the printed optical pattern printed in the funnel-shaped field shown in Figure 4 appears dark when viewed vertically. The brightness of the printed image gradually increases from the center toward the edges. When the top edge of the printed image is tilted horizontally away from the viewer, the dark areas appear to move toward the bottom. Tilting the image vertically to the right causes the shadowed portions of the image to appear to move in the opposite direction of the tilt.

The tapered magnetic field lines shown in Figure 6 cause the magnetic flakes to align in the opposite order to the tapered field. As a result of this orientation, the movement in the image is in the opposite direction to that produced by the funnel-shaped image. Flakes 214, dispersed in ink 212 and printed on substrate 211, are tilted along magnetic field lines 213, with their tops tilted toward the center of the field.

A printed image produced in a conical field produces an image with a bright center at a vertical viewing angle as shown in FIG7A . When the printed image is tilted with its top edge away from the viewer, as shown in FIG7B , the bottom portion becomes a bright area, contrary to the image in FIG5A . FIG7C shows a vertical tilt to the right, which shifts the bright area to the left.

An image or shape printed in an annular field would be similar to produce an image having the appearance shown in Figure 9. A cross-sectional view of the positions of particles arranged in an annular field is shown in Figure 8 .

The methods described above for arranging magnetically alignable flakes or particles can be applied to this image, where the magnetic structure can be printed over the entire area of the image or only fill a portion of the image, depending on the desired image.

Many of the magnetic structures described above can be applied to images printed with a linked loop pattern to enhance the security features of banknotes and other valuable documents.

Referring now to Figures 8 and 9, a novel, inventive, and highly surprising effect is achieved by using stacked magnets 801 and 802. The annular parabolic reflector is formed by two annular magnets of different radii stacked on top of each other. The resulting magnetic field, partially illustrated by line 803, differs significantly from that using a single magnet. The magnetic field lines near the corners of the upper magnet bend downward under the influence of the lower magnet. As a result, magnetic particles 804 near the corners of the upper magnet appear to be within a region of the field where the field strength is sufficiently high to provide a precise concave particle alignment along the applied magnetic field lines. Flakes 805 appear as oriented concavities transitioning from the outer edges to the center. The flakes are dispersed in ink 806 on a substrate 807. As shown in the figure, if the magnets are annular, the resulting printed image appears as a bright ring under a single light source. Under daylight, it is a broad blue ring. Under illumination from several light sources, as shown in the photograph in Figure 9, the printed image appears as a cluster of rings equal in number to the number of surrounding light sources. This embodiment functions as a light detector, where the image appears to the observer as a number of rings corresponding to the number of physically separated light sources reflected from the image. That is, for example, if three light sources illuminate the image, three separate rings are visible, and if n light sources illuminate the image, n separate rings are visible, where n is a positive integer. It should be noted that the thickness, size, and strength of the magnets can be varied depending on the specific desired image. For example, stacked magnets can have the same thickness and strength, but different diameters, or alternatively, one or more parameters can be varied.

Many of the magnetic structures described previously can be applied to images printed with geometric and illusory optical images to enhance their illusory properties. Figures 10A, 10B, 10C, 11, 12, and 13A illustrate examples of these images. The spiral image of Figure 10A printed in a field having an annular pattern has the appearance shown in Figure 10B.

The same spiral image in Figure 10A, when printed with a funnel-shaped field, has a very different appearance from the image shown in Figure 10B (see Figure 10C). After printing with an applied annular field, the illusory image shown in Figure 11 has a different appearance as shown in Figure 12. The annular magnetic field creates the illusion of ripples in the image.

Another linear illusion image is shown in FIG. 13B , where printing is performed in a tapered field to enhance the optical illusion feature in FIG. 13B .

The images shown in Figures 3 through 13B are all radially symmetric. In each image, the flakes are arranged in rings, with the flakes along a given ring forming the same angle with the substrate, their edges resting on the substrate. Adjacent rings have flakes forming different angles with the substrate. Furthermore, the flakes in a given ring have planar surfaces that intersect the planes of adjacent flakes. This can be clearly seen in Figure 14.

Returning now to Figure 14 (not drawn to scale, assuming large flakes for illustrative purposes), a computer graphic illustrates an arrangement of flakes, such as that shown in Figure 7B, for the cone image. Although all flakes are shown resting on a common planar substrate, each ring of flakes R1, R2, through Rn, has flakes along its orientation that make a unique, identical angle with the planar substrate. As can be seen in Figure 14, the flakes in the outer ring R1 are all tilted at the same angle relative to the substrate, while the flakes in ring R2 are at the same, slightly steeper angle with the substrate, such that the angle increases as one moves from ring R1 to R2 to Rn. Because the flakes along any given ring, R1, lie on a circle of a specific diameter, and because the flakes have planar faces, by definition, the planes defining their faces intersect with their nearest neighboring flakes lying on the same circle. For example, flakes 280a, 280b, and 280c have flat, planar faces where these planes intersect. Although all flakes contact the substrate, the cone image gives the observer the illusion that the cone protrudes from the paper or substrate on which it is deposited.

Referring now to FIG. 15 , there is shown a diagram of the same cone as in FIG. 14 , with a cross-section through the middle of the structure shown in another perspective view to illustrate the arrangement of the flakes. Here, the orientation of the flakes, or their tilt relative to the substrate, is shown to indicate the field lines generated by a magnet (not shown) beneath the substrate. For purposes of clarity and understanding, the flakes are shown as being substantially square, but in practice, the shape of the flakes may vary significantly unless square, hexagonal, or other specifically shaped flakes are used.

Reference is now made to FIG. 16 , which illustrates an axisymmetric, conical arrangement of magnetic particles dispersed within a thin layer of ink. Field lines 162 are used to illustrate a cross-section of magnetic field 160, but in reality, these lines form a sheet of lines along the direction in which the flakes are oriented. The magnetically orientable flakes 163 are shown arranged in concentric rings within ink medium 164, with the flakes arranged along the field lines in each ring forming different angles with respect to substrate 165, with the angle increasing toward the center. Gaps 166 in the figure are included for illustrative purposes only, making it easier to see the angle of the flakes relative to the substrate.

Returning now to FIG17 , there is shown a conical arrangement of magnetic particles 173 dispersed in a thin layer of ink vehicle 172 supported on a plate 171. Lines 174 drawn perpendicular to the particle surfaces are for illustrative purposes only and illustrate the angular relationship perpendicular to the sheet surface (hereinafter referred to as “normals”), where the lines perpendicular to the surface converge at a point defining an imaginary elliptical region 175 where the normals converge.

Referring now to FIG19 , a diagram is shown illustrating a conical arrangement of magnetic particles 196 in a conical magnetic field formed by placing a conical magnet 193 atop a substrate. Particles or flakes 196 in ink 192 are oriented with magnetic field lines 195. Reference numeral 194 indicates a cross section of the magnetic field from the conical magnet 193. The flakes are again oriented in concentric circles, with the flakes along each circle or ring forming the same angle with the substrate, and with the flakes in different rings forming different angles with the substrate.

FIG20A shows an alternative embodiment in which a conical arrangement of magnetic particles in a conical magnetic field is provided by placing a funnel-shaped magnet 202 beneath a substrate 201. Magnetic particles 205 in an ink carrier (not shown) are printed on a paper substrate 201. Reference numeral 203 represents a cross-section of the magnetic field, with the magnetic particles 205 following the magnetic field lines 204. Because the field lines 204 extend across the entire area of the substrate, the ink applied to the circular area with the flakes therein forms an arrangement. Thus, the circle of flakes 205 placed in the magnetic field, once aligned in the field, has the visual effect of viewing a conical object. This is captured in the photographs of FIG21A and FIG21B, which show a conical print tilted toward observer 1 and away from observer 2.

FIG. 20C shows a funnel-shaped arrangement of magnetic particles 209 dispersed in a vehicle comprising a thin layer of ink 207 and shows the surface normals 208 of the particles.

20D shows an alternative embodiment in which a funnel-shaped arrangement of magnetic flakes 236 is provided by a sphere or ball magnet 233 disposed beneath a paper substrate 231. The flakes 236, following the field lines 235, are disposed in an ink carrier 230. When the ink cures, the flakes are fixed in the position shown.

FIG22 is a partial cross-sectional view showing the arrangement of diffractive magnetic particles 220 in an axisymmetric conical magnetic field. The preferred orientation of the particles' grooves is toward the center of the cone. When placed in a magnetic field, the diffractive flakes behave like any other magnetic particles; they orient along the lines of the applied magnetic field. However, whereas flat magnetic flakes dispersed in a wet ink carrier orient themselves along the magnetic field lines with their longest diagonal lines, the diffractive flakes 220 orient themselves with their grooves defining a diffractive structure or grating oriented along the magnetic field lines. The axisymmetric arrangement of the diffractive particles produces silver-like areas surrounded by rainbow-colored borders or rings of different colors in a printed image.

Figures 23 and 24 are photographs of axisymmetric prints containing magnetic diffractive particles and tilted towards the viewer.

As described above, the flat magnetic particles in the wet ink carrier dispersed on the substrate surface align themselves along the magnetic field lines of an applied magnetic field via their longest diagonal lines. In contrast to flat platelets, under identical conditions, diffractive magnetic platelets orient themselves along the magnetic field lines via the orientation of their grooves, as shown in FIG25 . Each particle reflects and scatters incident light only in a particularly narrow direction. This selected orientation in a magnetic field and the narrow reflection and scattering of light from the diffractive platelet surface enable the production of unique printed images similar to known holographic kinegrams.

Previously, embodiments have been disclosed involving curved or circular arrangements of flakes, forming a new class of optical patterns. These patterns are characterized by the angular relationship of the flat or diffractive flakes to the substrate on which they are supported. Many of these patterns form Fresnel structures, such as Fresnel reflectors. For example, the conical and funnel-shaped structures described previously form convex and concave Fresnel reflectors. By using flakes made of absorbing materials, absorbing Fresnel structures can be made. By using reflective flakes, Fresnel reflectors can be printed on a substrate. Such Fresnel structures have applications as beam steering devices for electromagnetic radiation of various wavelengths in optics and other fields; for example, as printable focusing reflectors for antennas.

Reference is now made to Figure 26, which shows an axisymmetric hemispherical arrangement of magnetic particles 263 dispersed in a thin layer of ink 264. A cross section 261 of a magnetic field is shown, along with the propagation of field lines 262 emanating from a magnet 266 through a substrate 265. The desired magnetic field is achieved by rotating the magnet 266 in the direction of arrow 267.

FIG27 clearly illustrates the Fresnel-like reflective structure formed by magnetically aligned reflective flakes 273, wherein an imaginary line 274 is shown perpendicular to the surface of the flakes supported by a substrate 271 in an ink carrier 272, and intersects a centerline perpendicular to the centermost flake. Reference numeral 275 represents an imaginary projecting ray through the flakes or mirrors 273.

Figures 28A and 28B show photographs of a hemispherical convex mirror, wherein in Figure 28A the upper edge of the photograph is tilted toward the viewer, and in Figure 28B the upper edge of the photograph is tilted away from the viewer. The image formed in the printed convex Fresnel mirror is essentially the same as the image formed in a conventional convex mirror, and there is no compensation for their spherical aberration.

Turning now to FIG. 29 , a perspective view shows an axisymmetric convex arrangement of diffractive magnetic particles 292 dispersed in an ink layer. Flat particles can replace the diffractive particles. Particles 292 are applied to a substrate, such as a paper substrate 291. Region 293 is devoid of particles for illustrative purposes. Region 294 depicts the radial orientation of the particle grooves. Reference numeral 295 denotes the region where the particles are rotated about their normal and tilted relative to the substrate, while reference numeral 296 denotes the region where the circularly oriented grooves and the particle plane have the greatest inclination relative to the substrate.

When the diffractive platelet 292 is placed in a magnetic field, the platelets 292 are oriented with their grooves along the lines of the applied magnetic field. The particles in the area around the central axis 297 of the printed pattern have their planes parallel to the substrate surface. Many, but not all, of the particles in this area are oriented with their grooves toward the central axis of the printed pattern.

The size of radially arranged region is relatively small and depends on the size of the magnetic field applied to the printed pattern. It can be about 2/3 of the magnet width (if using a flat permanent magnet). The direction of groove and the layout of particle 292 change significantly with the change of the distance from the central axis. The second region of the printed pattern adjacent to and surrounding the radially arranged region of groove comprises particles rotating around their normal, wherein the normal is perpendicular to the line of the particle surface as shown in Figure 30, and the face of the particle is tilted relative to substrate. The particles in the second region rotate around their normal until groove forms a circular arrangement along the circular orientation region. Along with the increase from the center distance, all particles in this region are circular orientation. They tilt with the substrate at the maximum angle.

Reference is now made to Figure 30, which illustrates the position and arrangement of diffraction particles 302 within a single radial line of particles dispersed in an ink layer deposited on a substrate 301. In a first region, the lines perpendicular to the particle surface 303 are nearly perpendicular to the substrate. The directions between the diffraction orders 306 are 90 degrees to the direction of the particle's lines. In a second region, where the distance from the particle to the central axis 302 increases, the particles gradually rotate about their normals while tilting on the substrate, with their normals pointing outward from the printed image. The directions between the diffraction orders also change as the particles rotate. When the particles rotate 90 degrees about their normals, the grooves become oriented along a circle. The particles tilt on the substrate with their normals oriented outward from the printed image. The diffraction orders are also tilted and radially oriented. Reference number 307 represents the direction of the kth diffraction order of particles near the center of the printed image; reference number 308 represents the direction of the kth diffraction order of particles in the circular arrangement area; reference number 309 represents the direction of the mth diffraction order of particles near the center of the printed image; reference number 310 represents the direction of the mth diffraction order of particles near the center of the printed image.

Figure 31 is a photograph of a printed convex Fresnel mirror made with diluted ink on a black background. It shows a central silver region 311 with grooves oriented in radial directions. Adjacent to it is a rainbow region 312, where the rotation of the grooves produces strong, vibrant colors; the outer region 313 displays weaker rainbow colors. When an observer looks at the central region 311 and their viewing direction coincides with the orientation of the grooves, no diffraction of light is visible. When the observer views the image, a rainbow ring surrounds the silver region with radial groove orientation. The particles in the rainbow-colored region rotate about their normals, and these particles lie relatively flat on the substrate. As the grooves of the particles rotate, they change their orientation, and diffraction of light begins to produce a rainbow of colors. The tilt of the particles relative to the substrate surface in the outer region 313 causes a change in the direction of light reflected from the mirror surface. The observer cannot see the reflected light in this region because it is directed toward the bottom of the page. Only a few diffraction orders that produce a few rainbow colors are visible. The printed image is produced by coating the substrate with a black background. The flood layer of ink contains 5% flat magnetic particles with an average size of 20 microns and a diffraction grating frequency of 1500 lines/mm. The thickness of the printed layer is approximately 9 microns. The substrate with wet ink is placed on top of a spinning (3" x 1.25" x <0.375") permanent magnet. After the particles are aligned, the ink is cured under UV light.

Reference is now made to Figure 32, which shows an axisymmetric hemispherical arrangement of magnetic particles 323 dispersed in a thin layer of ink 324 printed in the form of a printed non-compensated concave Fresnel mirror on a substrate 325. Reference numeral 321 indicates a cross section having lines 322 emanating from a rotating magnet 326 in the direction of arrow 327.

Figure 33 is a diagram showing a concave arrangement of magnetic diffractive particles 333 having a grating of grooves dispersed in a thin layer of ink vehicle 332, with lines perpendicular to the particle surface 334. One area of spherical aberration 335 is just below the focal point 336 where the sheet is concave.

Figures 34A, 34B, and 34C are photographs of hemispherical arrays. Specifically, Figure 34A is a photograph with its upper edge tilted toward the viewer; Figure 34B is a photograph with its upper edge tilted away from the viewer; and Figure 34C shows the shadow of the photograph reflected from the printed mirror.

The image formed in a printed concave Fresnel mirror is essentially the same as the image formed in a conventional concave mirror, which has not been compensated for its spherical aberration. By correctly selecting the shape of the applied magnetic field and its strength, the distance between the magnet and the wet ink, the viscosity of the ink and the magnetic properties of the dispersed particles, the mirror can be compensated to reduce the aberration.

FIG35 is a plan view of an axisymmetric concave arrangement of diffractive magnetic particles dispersed in an ink layer, which is similar to FIG29 in many respects.

A substrate 351 is coated with diffractive particles 352 in an ink solvent (not shown). For illustrative purposes only, region 353 of the printed image is devoid of particles. Region 354 shows the radial orientation of the particle grooves. Region 355 is the region where the particles are rotated about their normal (i.e., a line perpendicular to the particle face), where they are tilted relative to the substrate; region 356 shows the circular orientation of the grooves, where the particle face is at its maximum tilt relative to the substrate.

The preferred orientation of the grooves of the particles is in the direction of the center of the cone. When exposed to a magnetic field, the diffraction platelets 352 are oriented through their grooves along the lines of the applied magnetic field. The particles in the area surrounding the central axis of the print are parallel to the substrate surface. Many particles in this area, but not all, are oriented through their grooves toward the central axis of the print. The size of this area is small, but it depends on the size of the magnetic field applied to the print. The orientation of the grooves and the layout of the particles will change significantly as the distance from the central axis changes. A second area of the print, adjacent to and surrounding the radially arranged area of the grooves, contains particles rotated around their normals as shown in Figure 36, with their faces tilted relative to the substrate. The particles in the second area rotate around their normals until the grooves are arranged in a circle. As the distance from the center increases, all the particles in this area are circularly oriented. They are tilted at the largest angle to the substrate.

Figure 36 shows the position and arrangement of diffraction particles 362 within a single radial line of particles dispersed in an ink layer. In the first region, lines 364 perpendicular to the particle surface are substantially perpendicular to the substrate 361. The directions between diffraction orders are 90 degrees to the direction of the particle lines. In the second region, where the distance from the particle to the central axis 363 increases, the particles gradually rotate about their normals while tilting on the substrate, with their normals pointing outward from the printed pattern. The directions 365 between diffraction orders also rotate with the rotation of the particles. When the particles rotate 90 degrees about their normals, the grooves become oriented along a circle. On the substrate, the particles tilt with their normals oriented outward from the printed pattern. The diffraction orders are also tilted and radially oriented. Reference numeral 366 indicates the direction of the kth diffraction order of a particle near the center of the printed pattern; reference numeral 367 indicates the direction of the kth diffraction order of a particle within the circular arrangement; reference numeral 368 indicates the direction of the mth diffraction order of a particle near the center of the printed pattern; and reference numeral 369 indicates the direction of the mth diffraction order of a particle near the center of the printed pattern.

An embodiment of the invention will now be described which relates to the production of a hemispherical image according to the invention.

An interesting and striking effect is shown in an alternative embodiment of the present invention in Figures 37F, 37G, 37H, and 37J. Figure 37F is a printed hemispherical image in which the entire image is coated with alignable pigment flakes. As will be explained, after the flakes are aligned, a hemisphere is formed. As the substrate is tilted or the light source is changed, the printed hemisphere shown in Figure 37F appears similar to the image shown in Figure 37G. As the image is tilted from normal through the center to the left about a vertical axis, the bright hemisphere, which appears more like a ball, rolls as the tilt angle changes. Unlike a scroll bar, which can scroll along a line in a plane, the hemisphere in Figure 37F can or appears to move in the x-y direction, depending on the tilt angle. Tilting the image about the x or y axis creates the appearance of movement.

The shield image in Figure 37J uses a combination of rolling bars and hemisphere effects to create a very interesting combination of effects, in which the shield image and hemisphere appear to protrude from the page. It is manufactured using a two-stage process, in which a substrate is first coated with a magnetic coating, the hemisphere is formed, and then cured, as shown in Figure 37H. A second coating is applied through a mask or stencil to form the coating of Figure 37I, ensuring that no additional coating material covers the hemisphere. The second coating is placed in a magnetic field to produce the rolling bars. The above-mentioned method of forming dynamic or moving images is more complex than the method of forming the rolling bars. This method will now be described with reference to Figures 37A to 37E. For example, the magnet 370a shown in Figure 37A shows field lines above and below the magnet, forming two loops. This figure intentionally only shows these two lines, however, in reality, many lines parallel to these lines are generated and pass through the entire magnet. Figures 37A, 37B, and 37C show the magnet at different times during rotation about a vertical axis. Part of the magnet in Figure 37B has been cut away to illustrate some of the field lines. In FIG37C , it is apparent that the field extending above magnets 370a, 370b, and 370c is dome-shaped, as is the field extending below the magnets. By coating substrate 377 with liquid ink in a dome-shaped magnetic field just above the magnets, as shown in FIG37D , a printed image of a hemispherical motion image is formed in FIG37E . As the magnets spin, the image separates further from the magnets and is supported toward the center of the field. In this exemplary embodiment, the magnets and image rotate relative to each other at a speed of approximately 120 rpm. The image is then removed from the field area and cured. The magnets can be rotated at a speed slower or faster than 120 rpm, depending on the properties of the magnetic particles and the viscosity of the ink carrier. However, if the speed is too slow, the image quality will be reduced.

FIG38A is a diagram of an alternative embodiment showing a simulated magnetic field from a hemispherical magnet. This is the shape of the field that produces the image shown in FIG38C. The north pole of the magnet is at the top, and the particles are arranged concentrically in a funnel-shaped manner. It shows the field 194 in FIG38B, with flakes 193 in a carrier 192 disposed on a substrate 191 arranged in a cone-shaped orientation following the field lines. In contrast to the hemispherical effect, the field produces a bright moving spot 192 in the center of the image 191; the funnel-shaped arrangement of the flakes produces a dark moving spot in the center of the image. Although the field shown and described is formed by a permanent magnet, in many embodiments, an electric field or an electromagnetic field can be used. Of course, the field and the particles must be compatible so that the particles can be oriented by the specific field. The particles can be diffractive and/or can be color-shifting.

Furthermore, for example, small magnetic microflakes with rectangular low-modulation low-frequency gratings can be used to make magnetic inks for printing images with optical effects.

As described above, the flat particles of reflective magnetic pigment dispersed in a non-curing coating or ink vehicle align themselves along the longest diagonal line through which the applied magnetic field passes; the diffractive particles dispersed in a non-curing coating or ink vehicle align themselves along their grooves in the direction of the magnetic field lines of the applied field because the demagnetization of individual particles is less along the grooves than across them.

This phenomenon is related to the cross-sectional thickness of the magnetic particles in different directions: it is smaller along the grooves and larger across them. The low specular reflectivity of incident light passing through diffractive pigments is due to their peculiar surface morphology. When printed, the pigments exhibit diffraction colors under single or multiple light sources and in sunlight. However, in dim light or under daylight, the printed image exhibits little color.

Another aspect of the present invention is to provide a pigment that combines two special features of reflective and diffractive pigments: high reflectivity without a noticeable diffraction color, and the ability to align the grooves along the magnetic field lines of an applied magnetic field. At low frequencies, the pigment has a microstructure that is a low-modulation square diffraction grating. Typically, the frequency can be in the range of 2 lines/mm to 500 lines/mm, more preferably in the range of 50 lines/mm to 150 lines/mm. The modulation of the grating varies in the range of 20 nm to 1000 nm (more preferably in the range of 30 nm to 200 nm).

FIG39 shows a plan view of a single pigment particle, and FIG40 shows a cross-sectional view thereof. The microstructured pigment according to the present invention can be manufactured from a microstructured magnetic material coated with an organic or inorganic protective coating, or from a microstructured polymer substrate coated with a magnetic material. More preferably, the microstructured pigment is manufactured from a microstructured magnetic material enclosed between two layers of reflective material. A typical embodiment of such a structure is shown in FIG41.

Example 1

A multilayer structure of _MgF2 /Al/Ni/Al/ _MgF2 was vacuum deposited on top of a polyester rectangular grating similar to that shown in Figure 39. The width of the grating peaks and valleys was 7 microns. The height of the peaks was 80 nm. The material was peeled off from the raised substrate and turned into micro-flakes with an average size of 24 microns.

The results were compared with those of the same optical multilayer stack deposited on a different polyester diffraction grating with a frequency of 1500 lines/mm before the _MgF2 /Al/Ni/Al/ _MgF2 coating was peeled off from the substrate. The color properties of the coatings on low-frequency and high-frequency substrates were measured using a goniospectrometer (Murakami Color Research Laboratories). The experimental results are shown in Figure 42.

The results in Figures 42a and 42b show that the low-modulation, low-frequency rectangular grating sample produces almost invisible diffraction color when measured across the grooves, and no diffraction color at all when viewed along the grooves (not shown in the figures). A direction across the grooves is most favorable for the formation of diffraction effects. A standard 1500 lines/mm sinusoidal diffraction grating (Figures 42a and b, 2) exhibits a significant color trajectory when viewed in this direction.

The spread of spectral reflectance near the normal angle of these two samples was measured using a Datacolor SF600 spectrometer. Figures 43 and 44 show the experimental results of %R, where (1) represents %R along the groove and (2) represents %R across the groove.

The results showed that the foil with the low-frequency grating had a silvery appearance. There were no color peaks in the reflectivity curve, either along the grooves or across them. In contrast, the high-frequency foil samples showed reflectivity peaks caused by diffraction of the incident light.

In general, if the frequency is low enough, for example less than 200 lines/mm and preferably less than 100 lines/mm, the diffraction effect is not visible to the human eye, however the grating advantageously allows alignment along the grating lines. The grating depth is preferably less than 100 nm.

The shape of the flakes used in the images described in the previous embodiments is hexagonal. In another embodiment of the present invention, a greater packing density of flakes can be used within the image, and it is also advantageous to provide uniform flakes. A description of making shaped flakes is disclosed in US Patent Published Application 20060035080.

Claims (23)

1. An apparatus relating to an image having an illusory optical effect, comprising an image having a plurality of at least n magnetically arrangable sheets stationary on a substrate in a first pattern; The plurality of magnetically arrangable thin sheets, numbering at least n, include: The first set of thin slices forming the first curve; and The second set of thin slices that form the second curve; At least 50% of the plurality of magnetically arrangable sheets, numbering at least n, are oriented such that lines perpendicular to their reflective surfaces converge along the lines or converge to a point. The first set of thin sheets are tilted at the same first angle relative to the substrate. The second set of sheets is tilted at the same second angle relative to the substrate. The first angle is different from the second angle; and Where n>1000. 2. The apparatus as described in claim 1, The planes extending from the surfaces of the plurality of magnetically arrangable sheets located on the first curve (at least n in number) intersect each other, and The planes extending from the surfaces of the plurality of magnetically arrangable sheets, numbering at least n, located on the second curve intersect each other. 3. The apparatus as described in claim 1 or 2, The plurality of magnetically arrangable thin sheets, numbering at least n, define a plurality of concentric rings of the thin sheet. The multiple concentric rings of the thin sheet form a circular region, and The plurality of magnetically arranged sheets, numbering at least n, form an increasing or decreasing angle relative to the substrate from the outermost ring of the plurality of concentric rings of the sheet to the innermost ring of the plurality of concentric rings of the sheet. 4. The apparatus of claim 1 or 2, wherein the planes extending along the surface of the second set of sheets intersect each other. 5. The apparatus as described in claim 1 or 2, The plurality of magnetically arrangable sheets, numbering at least n, are substantially distributed throughout the enclosed region and oriented therein in a predetermined pattern. 6. The apparatus of claim 1, wherein the planes of the first set of sheets and the second set of sheets intersect each other. 7. The apparatus of any one of claims 1, 2 and 6, wherein n > 10,000. 8. The apparatus of claim 3, wherein the image forms a Fresnel structure. 9. The apparatus as claimed in any one of claims 1, 2, and 6, The image described therein forms part of a receiving or reflecting antenna, and The plurality of magnetically arranged thin sheets, which are at least n in number, are absorbing or reflecting sheets. 10. The apparatus as claimed in any one of claims 1, 2, 6, and 8, The surface area of the plurality of magnetically arranged thin sheets, which are at least n in number, is between 100 ^μm² and 1 ^mm² . The thickness of the plurality of magnetically arranged thin sheets, which are at least n in number, is in the range of 100 nm to 100 μm. 11. The apparatus of any one of claims 1, 2 and 6, wherein the plurality of magnetically arrangable sheets, numbering at least n, are arranged in accordance with a magnetic field present throughout the circular region. 12. The apparatus of any one of claims 1, 2, 6 and 8, wherein the plurality of magnetically arranged sheets, numbering at least n, cover the entire circular region. 13. The apparatus as claimed in any one of claims 1, 2, 6, and 8, At least some of the plurality of magnetically arrangable thin sheets, which are at least n in number, have gratings therein or on them. The frequency and depth of the grating are low enough that they do not exhibit diffraction effects visible to the naked eye. The at least some of the plurality of magnetically arrangeable sheets, which are at least n in number, are arranged along the lines of their respective gratings. 14. The apparatus as claimed in any one of claims 1, 2, 6, and 8, At least some of the plurality of magnetically arrangable thin sheets, which are at least n in number, have gratings therein or on them. The frequency of the grating is less than 200 lines/mm, and The depth of the grating is less than 100 micrometers. 15. The apparatus of any one of claims 1, 2, 6 and 8, wherein the image is a cone-shaped, spherical, hemispherical or funnel-shaped image. 16. The apparatus of claim 1, wherein the image is formed in the form of a Fresnel structure of a printed reflective element array. 17. The apparatus of any one of claims 1, 2, 6, 8 and 16, wherein the plurality of magnetically arrangable sheets, numbering at least n, are uniform in shape. 18. The apparatus of any one of claims 1, 2, 6, 8 and 16, wherein two or more of the plurality of magnetically arrangable sheets, which are at least n in number, are hexagonal. 19. The apparatus of any one of claims 1, 2, 6, 8 and 16, wherein two or more of the plurality of magnetically arrangable sheets, which are at least n in number, have a diffraction structure thereon or on it. 20. The apparatus of claim 1, The image is an optically illusory image and has a rotation axis; the image includes at least one region of the substrate. The plurality of magnetically arrangable sheets, numbering at least n, are substantially distributed throughout the entire area of the substrate and oriented therein in a predetermined pattern. The plurality of magnetically arrangable sheets, numbering at least n, are oriented such that lines perpendicular to their reflective surfaces converge along the axis of rotation or converge to a point, and The rotation axis is perpendicular to the base. 21. An optical element comprising a plurality of concentric rings of magnetically arrangable sheets disposed on a substrate in a Fresnel structure, wherein at least 50% of the magnetically arrangable sheets are oriented such that lines perpendicular to their reflective surfaces converge at a single point. The magnetically arrangable sheet comprises: The first set of thin slices forming the first curve; and The second set of thin slices that form the second curve, The first set of thin sheets are tilted at the same first angle relative to the substrate. The second set of sheets is tilted at the same second angle relative to the substrate. Wherein the first angle is different from the second angle, and The number of magnetically arrangable thin sheets is >1000. 22. The optical element of claim 21, wherein the Fresnel structure is a Fresnel reflector. 23. The optical element of claim 21, wherein the Fresnel structure has no spherical aberration.